On the 25th anniversary of the b-quark discovery, Fermilab scientists recall overcoming a slow start

by Kurt Riesselmann

Research can be as dramatic as a sports tournament. Even if you are off
to a slow start, your team still can show a strong performance in the playoffs.

The discovery of the bottom quark, found twenty-five years ago at Fermilab,
is a case in point.

In the seventies, collaborators of the Fermilab experiments E70 and E288
were at the center of a drama that unfolded over a seven-year period.
It included such exciting times as the “November revolution” in 1974,
when experimental groups at Stanford and Brookhaven simultaneously
reported the discovery of a fourth type of quark, the charm.

By any luck, and with better timing, that discovery could have been made
at Fermilab.

“Fermilab unfortunately was just one step behind,” said John Yoh, who joined
Fermilab in the early seventies. “We had a new machine, and there were
several experiments that—if they had been further along—could have
discovered the J/Psi,” the particle composed of a charm quark and anti-quark.

The J/ Psi announcement came only nine months after scientists from
Columbia University and Fermilab decided to upgrade their experimental
apparatus known as E70 and proposed in a one-page letter to director
Robert Wilson that with the follow-up experiment, called E288, they would
search for particles like the W boson to “publish these and become famous.”
Their colleagues in California and on Long Island, however, were the first
to stand in the limelight.

“After the November revolution we at E70 realized that we had missed the
boat,” Yoh recalled.

But the experimenters at Fermilab were far from throwing in the towel.
They knew that Fermilab’s new Main Ring accelerator would eventually
be fifteen times more powerful than Brookhaven’s AGS ring, presenting a
huge window of opportunity to produce new, heavier particles.

“There was a huge mass region, totally unexplored,” recalled Leon
Lederman, the spokesperson of E70 and E288. “We were on a hunt for
vector mesons and anything new would have been welcome.”

By the spring of 1977, E288 experimenters had made another upgrade to
their experiment, collecting one thousand times more data than in 1975.
Fermilab’s first major discovery was just around the corner.

“After a few weeks with the new configuration,
we found that the probability to produce muonantimuon
pairs peaked sharply at about ten times
the proton mass,” said Dan Kaplan, who worked on
E288 as a graduate student and is now a physics
professor at the Illinois Institute of Technology.
“We were observing a new quark.”

The new result from Fermilab, soon identified as
the bottom quark, had a big impact.

“The discovery of the charm quark convinced
people that quarks are more than a mathematical
construct,” said Jeff Appel, who moved from
New York to Batavia to lead the E70 team as
Lederman’s deputy. “The subsequent discovery
of the bottom quark convinced people immediately
that there must be a third generation. There were
expectations that another quark—probably three
times heavier than the bottom quark—should
exist.”

Nature, however, made it more difficult for the
‘quark detectives’ to find the missing piece. It took
another eighteen years until scientists discovered
the bottom’s partner—the top quark, which was
twenty-five times heavier than the bottom quark.
Scientists had to wait for construction of Fermilab’s
Tevatron accelerator, completed in 1986, to create
collisions powerful enough to produce top quarks.
Why the tiny particles—first seen in 1994—are
as heavy as a gold atom is still one of the big
mysteries of the subatomic world.

Today, bottom quark physics is more important
than anyone could have imagined.

Collaboration members not shown in these photos: David Snyder (Columbia University, now Gallaudet
University), Taiji Yamanouchi (FNAL), Hans Jöstlein (SUNY, now FNAL), William Sippach (formerly
FNAL) and people from the Fermilab accelerator division.

“This Fermilab discovery has generated a huge
activity: two large new accelerators adding to the
Tevatron, which has been a workhorse of the
subject,” said Lederman, who shared the 1988
Nobel Prize for a neutrino experiment he carried
out at Brookhaven in 1962. “New major detectors
at Fermilab, DESY and CERN... I would think the
attention is flattering, matched only by neutrino
physics as the two HEP activities that stand outside
of pushing the frontiers of energy.”

Particles containing bottom quarks are the perfect
instrument to learn more about a tiny flaw in the
mirror-like behavior of matter and antimatter. The
imperfect symmetry, referred to as CP violation,
may be the key for why the universe has matter—
including the stuff we are made of.

“Yesterday’s discovery is today’s tool,” said Appel.
“Scientists have built B factories in California and
Japan to study this. And our Fermilab experiments,
CDF and DZero, should provide excellent answers,
too.”

Play by play, particle physics continues its success
story around the world.